Optimal Selection Of Nitrification Bacteria And Its Effects On Purifying Ammonia And Nitrite Nitrogen In Aquaculture Water

Ammonia and nitrite nitrogen tend to accumulate in intensive aquaculture water,resulting in deterioration of water quality,furthermore,seriously endangering the health of aquatic organisms.Therefore,it is the key to aquaculture water treatment that taking effective control of ammonia nitrogen,nitrite nitrogen and other harmful nitrogen contents in water.Typically,it mainly relys on physical,chemical and biological methods to remove ammonia and nitrite nitrogen in aquaculture water,among which the microbial method is gaining more and more attention.To date,applications of microbial techniques for ammonia and nitrite nitrogen treatment are generally focus on microbial preparation,biofloc technology,circulating water system,biological filter,biological carousel,biological drum,immobilized microorganism and so on.Wherein,microbial preparations are commonly used in aquaculture due to their ease of use,safe and non-toxic to aquatic organisms,and remarkable application effects.Moreover,nitrifying bacteria are considered to be the most effective group for the removal of ammonia and nitrite nitrogen.However,they grow and reproduce very slowly and they are sensitive to the environment stress.In practical application,it was found that most of the nitrifying bacteria had poor effect and functional stability on removal of ammonia and nitrite nitrogen,which need to be further studied.In this study,we selected two strains,XH1 and XH2,from the original nitrification bacteria that were previously obtained from the water of Litopenaeus vannamei intensive culture in our laboratory.Then single factor experiments were used to determine which one could grow better and remove ammonia and nitrite nitrogen efficiently.The conditions of different salinities(5,15,25,35 and 45),pH values(4.5,6.0,7.5,9.0 and10.5),temperatures(5,15,25,35 and 45?)and aeration levels(1 and 2L/min)were adopted,seperately.Upon optimization,the candidate strain XH2,the bacterium Rhodopseudomonas palustris,the bacterium Lactobacillus casei and the nitrification bacteria were separately used or combined in certain manners to treat high nutrient aquaculture water.Their effects on removing ammonia and nitrite nitrogen,as well as their growth characteristics,were examined.This study provides scientific basis and support for the further development of functionally stable aquatic nitrification products.The results are as follows:1.Strain XH1 had comparatively extensive adaptability to salinity(5~45),pH(6.0~9.0),temperature(15~45?)and ventilation(1~2 L/min),with a maximum observed cell amount of 2.34×10~9 cells/mL.Especially,the concentration of ammonia nitrogen in medium reduced by 86~97%during 1~3 days under the salinity of 5~35,pH of 6.0~9.0,temperature of15~30?and the ventilation volume of 1 L/min(P<0.05).However,the concentration of ammonia nitrogen in medium decreased at first and then it increased.The concentrations of nitrite nitrogen showed no significant difference.Strain XH1 was identified as Citreicella thiooxidans.2.Strain XH2 had comparatively extensive adaptability to salinity(5~45),pH(6.0~9.0),temperature(15~45?)and aeration levels(1~2L/min),with a maximum observed cell amount of 1.03×10~9 cells/mL.Emphatically,the concentration of ammonia nitrogen in medium reduced by 90~100%during 1~3 days under the salinity of 25~45,pH of 6.0~9.0,temperature of 15~30?and the ventilation volume of 1~2 L/min(P<0.05).Meanwhile,the concentrations of nitrite nitrogen showed no significant difference.Strain XH2 was identified as Rhodococcus rhodochrous.Taken together,strain XH2 has good environmental adaptability and its removal effect on ammonia nitrogen is better and more stable than strain XH1,which indicates that strain XH2 can be used as an ideal alternative strain for the research and development of bacterial products for ammonia nitrogen prevention and control in aquaculture.Therefore,it was determined as a preferred strain for subsequent experiments.3.The efficiency of removing ammonia and nitrite nitrogen by group nitrification bacteria was high,with the good stability.Group XH2 was slightly inferior to the group nitrification bacteria on the efficiency and stability of removing ammonia nitrogen,while group Rhodopseudomonas palustris and group Lactobacillus casei had no significant effect on removal of ammonia and nitrite nitrogen.During the compatibility experiment,the combination of strain XH2 or Rhodopseudomonas palustris with the nitrification bacteria could significantly increase the removal efficiency of ammonia nitrogen,which was stable during the experiment period.In contrast,the effect of group strain XH2 combined with nitrification bacteria is better.To some extent,however,Lactobacillus casei inhibited the ability of nitrification bacteria for removing ammonia and nitrite nitrogen.To sum up,combined with strain XH2 or Rhodopseudomonas palustris can help strengthen the application of the nitrification bacteria.By the way,when the ratio of nitrification bacteria transferred in water is low,it will take a longer time to remove ammonia and nitrite nitrogen to a lower level.At the same time,its ammonia nitrogen removal effect is significantly weakened,however its nitrite nitrogen removal effect is less affected.